Project Summary/Abstract: The ubiquitously expressed antioxidant enzyme manganese superoxide dismutase (MnSOD), encoded by the gene SOD2, has been implicated as having a role in cancer initiation and/or progression;however, it remains unknown whether loss of MnSOD in vivo is sufficient to drive or enhance the carcinogenic process because of the very short life spans of the systemic constitutive SOD2-/- mice. In addition, MnSOD expression is altered in cancer cells compared to their normal cell counterparts, and epigenetic mechanisms are emerging as important regulators of MnSOD expression in multiple types of cancer. In this proposal, these mechanisms will be examined in detail in human breast carcinoma cells. We hypothesize that 1) MnSOD expression is governed at least in part based on the epigenetic landscape of the SOD2 gene;2) induction of MnSOD expression in tumor and normal cells is accomplished at least in part through chromatin structural rearrangements involving discreet regulatory regions of the SOD2 gene;3) SOD2 has a role as a tumor suppressor gene in vivo. These hypotheses are connected by our overall objective to understand the molecular genetic and epigenetic control mechanisms governing MnSOD expression in human cancer and its involvement in modulating the malignant phenotype. This objective will be achieved through pursuit of the following specific aims: Aim 1. Identify and characterize how changes to chromatin accessibility, histone modifications, cytosine methylation and transcription factor binding in vivo at the human SOD2 locus alter MnSOD expression patterns and affect characteristics of the malignant phenotype in human breast cancer cells compared to normal human mammary epithelial cells. Aim 2. Determine whether induction of MnSOD mRNA expression in tumor or normal cells involves chromatin structural rearrangements that include a physical interaction exists between the intronic enhancer and 5' regulatory regions of SOD2. Aim 3. Determine the causal role of MnSOD in mammary carcinogenesis and thymic lymphomagenesis using cell type specific knockout of SOD2 in mammary epithelial cells and T lymphocytes respectively in conditional knockout floxed SOD2 mice.